This is a 3 part question..
I'm designing a patio enclosure with many windows and narrow shearwalls using FTAO for a restaurant addition/expansion. This is adding on to an old stucco/plaster wood frame building, an old gas station built as late as the 40's. The patio, extending 18' off the existing building was built in the 80's and stands on 4"x6" posts open to the outside. They want to enclose the patio, not wanting to go conventional because of the existing 2'x2' post footings instead of chipping out the existing slab perimeter and pouring a perimeter foundation.
If the new shearwalls of the enclosure are the same stiffness as the old, RAM shows no increase in stress for the old exterior wall from taking the old lateral cantilevered patio roof forces, to the new enclosed system with the additional shearwalls. But I don't know if the stiffnesses will be the same, or higher or lower. The building official has said it's ok for me to design it as a stand-alone structure, (ignoring the r-value of the old construction?) even letting me design for eq only in the direction that saw no increase in the surface area for wind. I don't feel comfortable taking those liberties with how many unknowns there are with the old building.
1. I wanted to confirm that the only response modification factor, r-value, I can use is controlled by the the old construction as 2 for lightweight-other, whether the old system is for stucco shearwalls or let-in braces. (unknown, assuming let-in braces) Per ASCE 7-05 22.214.171.124 "R, Cd, and Overstrength Values for Horizontal Combinations"
2. I can't make it work for an r-value of 2 unless I can make the old pier footings not pinned at the top.. any ideas? I was thinking of pouring concrete inside the bottom of the new shearwalls even up to the window sill and doweling out of the 2x2 piers to fix them from rotation and add weight for overturning. At least for one direction.
3. Or should I recommend they go conventional? (and waive my fee)
This is my first side-project, which is fun and am learning a lot, but not so fun when I can't give them the answer they want to hear. I've already spent a month because this is my first, and I'm about half way done, and they're wanting me to be done yesterday.